Commonly known forms of apparatus of this type incorporate a fixed lower electrode, and an upper electrode which is movable either in a vertical direction, or which is pivoted about a fixed horizontally arranged axis for it to swing vertically about the radius of the pivot. In such known forms of apparatus, access of the workpiece to the nip of the electrodes is limited to movement of the workpiece in a generally horizontal direction into the nip of the electrodes, with the possibility of the workpiece impacting on one or other of the electrodes, with consequential damage to the electrodes.
In an attempt to provide more ready access of the workpiece to the nip of the electrodes, it has been proposed to support the upper electrode on a linkage which includes dual horizontally arranged pivots in order to increase the opening of the nip, and thus increase accessability of the workpiece to the nip.
Such a structure is, however, cumbersome, complicated and large in size, and consequently is expensive to manufacture. Additionally, in prolonged use, difficulty is experienced in ensuring the perfect alignment of the axis of the respective electrodes upon closing of the nip, the tendancy being for the movable upper electrode to move or wander laterally due to wear in the linkage and the bearings thereof, such that the axis of the upper electrode may be of set laterally to the axis of the fixed electrode, with consequent imperfections in the spot weld formed in the workpiece.